Radial Wind Speed Research Articles

Confidence interval estimation for VHF Doppler radar measurements of wind velocities

Linear model theory is used to find exact confidence intervals for wind components from radial wind speeds observed using a VHF Doppler radar. The theory is also used to evaluate exact confidence intervals for wind direction. However, exact confidence intervals for wind speeds can only be found where the errors in the two estimated horizontal wind speed components are equal. Thus, in the general case, a Taylor expansion has to be used to give approximate confidence intervals for wind speeds. It is shown that irrespective of the wind vector, the mean confidence interval for the wind components, or the confidence volume of the wind vector, can be minimized by using radar beams with the largest off‐vertical angles. However, there is no optimal sounding strategy for the measurement of wind speed or direction that can be defined before making any measurements.

Three‐dimensional steady compressible perturbations in the magnetohydrodynamic solar wind

We present a steady three‐dimensional magnetohydrodynamic (MHD) perturbation formulation for inhomogeneous solar wind stream structures. We derive analytical solutions for asymptotic behaviors of three‐dimensional compressible MHD perturbations at a large radial distance r in a background radial wind of spherical symmetry. There are three independent perturbation solutions at large r. In contrast with a three‐dimensional propagation of Alfvénic perturbations in the same kind of background wind, the magnetic field perturbation associated with a steady compressible MHD perturbation does not dominate the background radial magnetic field at large r. Since the three independent compressible MHD perturbation solutions are related by the two regularity conditions at the MHD slow and fast critical points, the leading asymptotic radial scalings of the relevant compressible MHD perturbation variables are the same as those of the background variables at large r. In other words, while the radial variations of compressible MHD perturbations gradually merge into the background MHD wind at large r, the distinct angular variations of the perturbations persist throughout the wind. To complement these analytical analyses, we obtain complete numerical solutions in the entire radial range, which smoothly pass through the MHD slow and fast critical points. We provide numerical examples in which the perturbation increase (or decrease) of the radial wind speed can be as large as ∼ 100 km s−1 due to the perturbation increase (or decrease) of the temperature above the coronal base while the solar wind mass flux variation remains sufficiently small. This is possible because of our three‐dimensional approach and because of the regulation mechanism of the magnetic field in the wind. We also present an axisymmetric model for steady MHD solar wind structures in the presence of solar differential rotation.

Measurement of winds in Venus' upper mesosphere based on doppler shifts of the 2.6-mm 12CO line

Before inferior conjuction in 1988, we observed Venus at the first rotational transition of 12CO using the three-element, millimeter-wavelenght array at the Owens Valley Radio Astronomy Observatory and successfully detected winds in the upper mesosphere of Venus. The subearth point occurred at 19.3 hr local Venus time and the planet's disk showed the evening terminator. The 33″.4 diameter disk was resolved by a synthesized beam 2″.8 at full-width-half-maximum. The absorption line was finely sampled in frequency by a 32-channel filterbank with channel widths of 50 kHz. With this spatial and spectral resolution, it was possible to measure doppler shifts of the absorption line across the planet due to strong winds in Venus' upper mesosphere. Weighting functions show sampling of the mesosphere within a 12-km-wide layer centered at 97 km at normal incidence in the evening, 99 km on the dayside limb, and 103 km on the nightside limb. The doppler shifts change in a manner indicative of westward, horizontal winds—being strongly blue on the east/dayside limb, zero near the center, and strongly red on the west/nightside limb of the planet. Measurements of these shifts along the planet limb are closest to direct measurements of the horizontal speeds once corrected for incidence angle. The mean value along the dayside limb is 85 ± 8 m sec −1 and along the nightside limb is 106 ± 10 m sec −1. The radial wind speeds from the doppler shifts were smoothed to reduce noise and then fitted in a least-squares sense to canonical forms of the lower atmosphere's westward zonal flow and the thermosphere's subsolar-to-antisolar flow. The two flows are highly correlated in orientation in these observations of Venus' evening terminator. The smoothed measurements are best fitted for zonal flows in 10° latitude bins from 70°S to 61°N. The mean value of these fitted zonal flows is 132 ± 10 m sec −1. No facet of the data exists to firmly support or rule out the existence of a smaller (≤40 m sec −1) subsolar-to-antisolar flow in the upper mesosphere.

Doppler-Radar Analysis of a Tropical Cyclone over Land: Hurricane Alicia (1983) in Oklahoma

Abstract The center of the circulation of the remains of Hurricane Alicia passed to the west of the National Severe Storms Laboratory's Doppler radar in Norman, Oklahoma on 19 August 1983. Three types of mesoscale precipitation were noted: the central area, principal rainband, and outer band. The central area and principal rainband were relatively stratiform, and the outer band was cellular. The maximum radial wind speed in the storm of 25–30 m s−1 was found in the principal band, and was probably in part a consequence of latent-heat release. The principal rainband, located to the cast and southeast of the storm's center, was responsible for much of the heavy rainfall over central Oklahoma, especially during the evening and nighttime hours, in response to low-level warm advection south of the cyclone late in the afternoon. We obtained a mesoscale, dual-Doppler analysis of the wind field at low levels from two single-Doppler radar volume scans recorded two hours apart. The basis of the analysis technique i...

Interplanetary gas. XX - Does the radial solar wind speed increase with latitude

view Abstract Citations (22) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Interplanetary gas. XX. Does the radial solar wind speed increase with latitude? Brandt, J. C. ; Harrington, R. S. ; Roosen, R. G. Abstract The astrometric technique used to derive solar wind speeds from ionic comet-tail orientations has been used to test the suggestion that the radial solar wind speed is higher near the solar poles than near the equator. We find no evidence for the suggested latitude variation. Publication: The Astrophysical Journal Pub Date: March 1975 DOI: 10.1086/153478 Bibcode: 1975ApJ...196..877B Keywords: Astrometry; Astronomical Coordinates; Comet Tails; Interplanetary Gas; Solar Wind Velocity; Astronomical Models; Azimuth; Latitude; Radial Distribution; Spatial Distribution; Solar Physics full text sources ADS | Related Materials (23) Part 1: 1959ApJ...130..670B Part 2: 1960ApJ...131...47C Part 3: 1961ApJ...133..675C Part 4: 1961ApJ...133..688B Part 5: 1961ApJ...134..394B Part 6: 1961ApJ...134..975B Part 7: 1962ApJ...136.1023B Part 8: 1966ApJS...13..125B Part 9: 1967ApJ...147..201B Part 10: 1967ApJ...148..905B Part 11: 1970ApJ...159.1057B Part 12: 1969ApJ...156.1117B Part 13: 1972ApJ...177..277B Part 14: 1973ApJ...183.1037B Part 15: 1973ApJ...184...27B Part 17: 1975ApJ...199..756P Part 18: 1978ApJ...223..655N Part 19: 1978ApJ...221.1014N Part 20: 1979ApJ...234..723N Part 21: 1980ApJ...241..820N Part 22: 1981ApJ...245.1159N Part 23: 1981ApJS...46..141N Part 24: 1982ApJS...48....1N